Hmmm... This topic reminds me of the movie "Clear and Present Danger" based on the book of Tom Clancy where a group of US special forces start an undercover war against the Cali Drug Cartel.
This could be interesting. Put on one side the Colombian Army, On the other the FARC, ELN or maybe a faction of Mercenaries fighting for a Drug Cartel.
Like it has been mentioned before... the combat would be similar to insurgency where the colombian Army would have to find weapons cache, cocaine labs or even the small transport aircrafts used to cargo the drugs; and destroy them.
All maps would be Jungle and mountain based... and I'm talking about a real deep jungle enviroment. With the woodland camouflages it'll be pretty hard to find the enemy without being caught first.
As for Hostage rescue... well... I don't know if the BF2 engine can support a combat modus where hostages are involved like in CS. =/
Maybe forcing the Colombian Army faction to have a third of its kits as VIPs kits putting them as the hostages and spawning only in the same area where FARC spawns. The rest of the Colombian Amry would have to kill all FARC soldiers and take the hostages to a safe base.
Hostage killing would have to be highly penalized for both factions but also there should be a penalization for the hostage if he gets killed... otherwise players that play as hostages would run out freely without suffereing consequences. But of course the role of the hostage would be awesomely boring... I mean the only mission of the hostage would be to survive.
Well... Hostage rescue is not something that BF2 was ment to replicate.
The following is purely a theory:
If another community made a Venezuelan or some Communist/Socialist Coalition of South American Armies, then that could represent another OPFOR for the colombian military.
One thing that should be noticed is that Venezuela is currently purchasing tons of new weaponry (Mostly from Russia). Most of this new equipment actually puts Venezuela in the position to resist or launch a conventional warfare. Colombia on the other hand purchases normally equipment ment to fight the guerrillas. Ergo Colombia doesn't have much need for Fighter jets, MBTs or other heavy weaponry that Venezuela is currently adquiring.
Well... the idea would be a Venezuelan or a similar fictional or real SA faction invading Colombia (Or the other way around). This scenario could also include US forces in south america.

with the Colombian side without many advantages.